1. Field of the Invention
The present invention relates to a process for producing a semiconductor article, specifically to a process for producing a semiconductor article by applying crystal formation treatment to a substrate having a free surface on which a nonnucleation surface exhibiting a smaller nucleation density and a nucleation surface exhibiting a larger nucleation density and having a sufficiently minute area so as to allow only a single nucleus to be formed thereon are disposed next to each other, whereby a monocrystal is permitted to grow from the nucleus.
The present invention is applicable to the formation of monocrystals, polycrystals, etc. for electronic devices, optical devices, magnetic devices, piezoelectric devices, surface acoustic devices, etc. including semiconductor integrated circuit, optical integrated circuit, magnetic circuit, etc.
2. Related Background Art
In the prior art, monocrystalline thin film to be used for semiconductor electronic devices, optical devices, etc. has been formed by epitaxial growth on a monocrystalline substrate. However, for epitaxial growth of monocrystalline thin film on a monocrystalline substrate, it is necessary to take into account the matching in lattice constant and coefficient of thermal expansion between the monocrystalline materials of the substrate and the epitaxial growth layer, and there has been involved the problem that the kind of substrate material is limited to an extremely narrow scope for formation of monocrystalline layer capable of providing a device of good quality.
Further, in recent years, research and development have been actively done about three-dimensional integrated circuits for accomplising high integration and multi-functionality by forming semiconductor devices by lamination in the direction normal to the substrate, and also research and development about large area semiconductor devices such as solar battery in which elements are arranged in an array on an inexpensive glass or switching transistor for liquid crystal picture elements, etc. are becoming more active year by year.
What is common in these researches and developments is that the technique to form a semiconductor film on an amorphous insulating material and form an electronic device such as transistor, etc. thereon is required. Among them, it has been particularly desired to have a technique to form a monocrystalline semiconductor film of high quality on an amorphous insulating material.
However, generally speaking, when a thin film is formed on an amorphous insulating substrate such as SiO.sub.2, etc., due to deficiency of long length order of the substrate material, the crystal structure of the deposited film will become amorphous or polycrystalline, whereby it is very difficult to form monocrystalline semiconductor of high quality. Here, amorphous film refers to one with the state in which although short length order to such an extent as the minimum order of neighbor atoms may be maintained, there is no particular order of longer length, while polycrystalline film refers to one in which monocrystal grains having no specific crystal direction are gathered as separated with grain boundaries.
As a solution of the problems as mentioned above in the prior art, European Patent Application EP 244081A1 proposes a method for forming crystal by preparing a substrate having a nonnucleation surface having a small nucleation density and a nulceation surface having a sufficiently larger nucleation density than the nonnucleation surface and a minute area such that only a single nucleus can be formed, then forming a single nucleus on the nucleation surface and permitting a monocrystal to grow from the single nucleus as the growing center, and it is shown possible to form a monocrystal even on the substrate surface of amorphous material by use of the above method.
On the other hand, semiconductor devices such as MOS type transistor, bipolar transistor, SCR, etc. are constituted of a plural number of p-n junction portions formed in combination. For example, in the case of a p-channel MOS type transistor, the device is constitutied of p-type semiconductor regions as source region and drain region formed in an n-type semiconductor region.
To form such a semiconductor device on an insulating amorphous substrate by use of the crystal forming method described in the European Patent Application EP 244081A1, a facet of monocrystal is permitted to grow on the substrate, and after flattening of the facet of monocrystal, the conventional semiconductor device production process is practiced. More specifically, after a certain conduction type semiconductor region is formed, ion implantation of n-type impurity or p-type impurity is practiced.
However, the above semiconductor device formation requires ion implantation and diffusion steps thus being complicated while it involves essential difficulty in separate formation of semiconductor regions with high precision which may be attributed to the difficulty in controlling the diffusion process.